ABUJA - Nigerian police fired shots and tear gas at thousands of supporters of an imprisoned Shi'ite cleric in Abuja on Tuesday, just a day after three people were killed in similar clashes that sparked warnings to the government that a heavy-handed crackdown could radicalize the group.
At least six Islamic Movement of Nigeria (IMN) supporters have now been killed since Saturday during protests calling for the release of Ibrahim Zakzaky, who has been in custody since December 2015.
Several thousand IMN members were marching peacefully in central Abuja but then armed police fired into the crowd to disperse the procession, said AFP reporters at the scene.
At least six injured IMN members were taken away in cars while the area was patrolled by dozens of police, they added.
"A lot of our people had been injured, so far we don't have any record of death," IMN spokesman Ibrahim Musa told AFP.
Nigeria's military said three IMN supporters were killed during another protest on the outskirts of Abuja on Monday.
The army said troops and police "repelled the attack" and that IMN "fired weapons" and threw stones and Molotov cocktails.
AFP photographs of the aftermath showed several bodies of civilians on the ground near police but it was unclear whether they were dead or injured.
On Saturday, three other IMN members were killed during protests in Abuja.
The army claimed the protesters attacked a military convoy and tried to steal weapons and ammunition — an account the IMN "categorically" denies.
IMN spokesman Musa claimed 27 people have been killed since Saturday and that the death toll could be higher since "scores" of people were injured and troops took away others.
"We are working towards their release to us for burial," Musa said.
Human rights group Amnesty International said on Monday that reports that troops fired live bullets at protesters were "very disturbing" and would be unlawful if they were unarmed.
The IMN has staged a series of demonstrations demanding the release of leader Zakzaky, who has been detained since bloody clashes broke out in the northern city of Zaria in 2015.
Then, the military was accused of killing more than 300 IMN supporters and burying them in mass graves.
Zakzaky has been at loggerheads with Nigeria's secular authorities for years because of his calls for an Iranian-style Islamic revolution. Northern Nigeria is majority Sunni Muslim.
The cleric, who is in his mid-sixties and lost the sight in one eye during the 2015 clashes, has been seen in public only twice since he was detained.
Nigeria's government has previously ignored a court order to release Zakzaky and his wife.
In April, at least 115 IMN supporters were arrested during protests in Abuja during which police used tear gas and water cannon.
IMN processions for the annual Ashura festival have frequently been flashpoints. In November 2016, at least 10 people were killed when police opened fire near the northern city of Kano.
Sustained clashes and the military's use of deadly force have raised fears of a repeat of the 2009 crackdown on the Islamist group Boko Haram in northeast Nigeria.
Then, some 800 people, including Boko Haram leader Mohammed Yusuf, were killed in the Borno state capital Maiduguri, forcing the group underground.
They then re-emerged a more deadly force under Yusuf's deputy, Abubakar Shekau. The insurgency since then has killed more than 27,000 people and displaced more than two million others.
Amaechi Nwokolo, a security analyst at the Roman Institute for International Studies in Abuja, said: "It appears we are not learning from our past mistakes."
He said the security forces had "no right to use that maximum force" on unarmed protesters, warning that it might "motivate others to radicalize".
"If we go back to the formative days of Boko Haram, it was the killing of some innocent people that actually galvanized recruitment. That's how terrorism works."
Nigeria's President Muhammadu Buhari, a former military ruler, was elected in 2015 on a promise to defeat Boko Haram and bring greater security.
But although weakened, Boko Haram has persisted in its attacks. In addition, there has been a resurgence of violence in the long-running resources conflict between sedentary farmers and nomadic herders.